Sealing around rotating or reciprocating shafts is performed in numerous ways. Sealing moving shafts is difficult in high pressure, dynamic operations, such as at high differential pressures and relatively high shaft rotational speeds typical in drilling operations. In general, the contact stress between the seal and shaft increases with increasing differential pressure. With lip-type seals, as the pressure differential across the seal increases, the differential pressure acts on the unsupported area of the sealing element or lip to create a high force, especially a high radial force, on the stationary sealing element acting against the rotating shaft. At some point, the lip can deform, extrude, or heat up to the point of leakage or failure.
Applications in oil well drilling subjects seals to high differential pressures. For just one example, a turbine in some circumstances operates between 1,000 and 6,000 rpm at differential pressures of approximately 3,000 PSI.